Polymer Brushes Research Articles

Nanoengineering Spikey Surfaces: Investigation of Reversible Organizational Control of Surface-Tethered Polypeptide Brushes.

Nature serves as an important source of inspiration for the innovation and development of micro- and nanostructures for advanced functional surfaces and substrates. One example used in nature is a spikey surface ranging from micrometer-sized spikes on pollen grains down to the nanometer-scale protein spikes found on viruses. This study explored the realization of such highly textured surfaces via the nanoengineering of self-assembled poly(γ-benzyl-l-glutamate) "nanospikes", exploiting solvent-induced chain organization, controlled surface chemical functionality, and enhanced stability in the form of polymer brushes. The reversible solvent-responsive behavior of these polymer chains and the aggregation behavior of the chain-ends were investigated via fluorescence characterization and studied through molecular simulations. Vapor-based solvent treatments were developed for orientation control with in situ analysis to understand film response and brush organizational behavior under different selected conditions. The effect of sub-100 nm nanopatterning on surface morphology and chain organization was examined via an integrated approach of experimental and computational studies. The methodologies established in this study present opportunities for engineering sophisticated nanoscale spikey surfaces with high customizability by means of nanolithography combined with solvent-assisted treatments.

Scalable Macroscopic Engineering from Polymer-Based Nanoscale Building Blocks: Existing Challenges and Emerging Opportunities.

Natural materials exhibit exceptional properties due to their hierarchical structures spanning from the nano- to the macroscale. Replicating these intricate spatial arrangements in synthetic materials presents a significant challenge as it requires precise control of nanometric features within large-scale structures. Addressing this challenge depends on developing methods that integrate assembly techniques across multiple length scales to construct multiscale-structured synthetic materials in practical, bulk forms. Polymers and polymer-hybrid nanoparticles, with their tunable composition and structural versatility, are promising candidates for creating hierarchically organized materials. This review highlights advances in scalable techniques for nanoscale organization of polymer-based building blocks within macroscopic structures, including block copolymer self-assembly with additive manufacturing, polymer brush nanoparticles capable of self-assembling into larger, ordered structures, and direct-write colloidal assembly. These techniques offer promising pathways toward the scalable fabrication of materials with emergent properties suited for advanced applications such as bioelectronic interfaces, artificial muscles, and other biomaterials.

Atomistic Simulations of Hydration and Antibiofouling Behavior of Amphiphilic Polymer Brush Surfaces Functionalized with TMAO and Short Fluorocarbon.

Developing fouling-resistant materials is of paramount interest in marine industries and biomedical applications. In this work, we studied the interfacial hydration and surface-protein interactions of the amphiphilic brush surface functionalized with hybrid hydrophilic trimethylamine N-oxide (TMAO) and hydrophobic pentafluoroethyl groups using a combination of atomistic molecular dynamics simulations and free-energy computations. Our results show that while the interfacial hydration density of the amphiphilic surface slightly decreases with the introduction of small fluorocarbons compared to that of the pure TMAO-functionalized surface, the amphiphilic surface remains relatively strong in resisting protein adsorption. The nanosized clustering of hydrophobic fluorine atoms on the top of the amphiphilic brush surface introduces weak protein adsorption; however, due to the strong interfacial hydration and weak hydrophobic interaction, the amphiphilic surface exhibits sufficient antibiofouling activities. Our fundamental studies will be critical for the discovery of marine fouling-resistant coating surfaces.

Scattering-Free and Fast Response Polymer Brush-Stabilized Liquid Crystals Beam Steering Using Surface-Initiated Polymerization Technique.

Nonmechanical fast response optical beam steering technology is increasingly essential for telecommunications, imaging systems, optical sensing, displays, and military applications. Polymer network liquid crystal (PNLC) beam steering can achieve submillisecond response times but faces limitations due to scattering issues arising from the refractive index mismatch between the polymer network and the liquid crystals (LCs). In this article, we demonstrate a scattering-free, fast-response LC beam steering by using polymer brushes to stabilize the gradient refractive index. First, the initiator is incorporated into the alignment layer and the monomer is mixed into the LC layer. Surface-initiated polymerization (SIP) is then employed to grow the polymer brushes exclusively on the substrate's surface, thus confining the polymer network's growth to the LC bulk and reducing interfacial scattering. For polymer brush stabilized liquid crystal (PBSLC) beam steering device with a period size of 225 μm and a cell gap of 7.2 μm, the average transmission rate reaches 88% in the visible light spectrum with a haze value of only 6.91. The steering angle is 0.16, and the diffraction efficiency is 80.3%. When a voltage of 35 Vrms is applied, the primary energy can be tuned to the zeroth order, with a response time close to 1 ms. By cascading two PBSLC beam steering devices with opposite steering directions, the primary energy of the beam can be adjusted between zeroth, +1, and -1 order. This method requires only a UV light source, a precision displacement stage, a power supply, and a mask, avoiding the need for expensive equipment and complex electrode fabrication. By adjustment of the phase change period, step width, and number of steps during fabrication, the steering angles and diffraction efficiency of the PBSLC beam steering device can be easily controlled, highlighting its significant potential for industrial production.

The Kinetics of Polymer Brush Growth in the Frame of the Reaction Diffusion Front Formalism

We studied the properties of a reaction front that forms in irreversible reaction–diffusion systems with concentration-dependent diffusivities during the synthesis of polymer brushes. A coarse-grained model of the polymerization process during the formation of polymer brushes was designed and investigated for this purpose. In this model, a certain amount of initiator was placed on an impenetrable surface, and the “grafted from” procedure of polymerization was carried out. The system consisted of monomer molecules and growing chains. The obtained brush consisted of linear chains embedded in nodes of a face-centered cubic lattice with excluded volume interactions only. The simulations were carried out for high rafting densities of 0.1, 0.3, and 0.6 and for reaction probabilities of 0.02, 0.002, and 0.0002. Simulations were performed by means of the Monte Carlo method while employing the Dynamic Lattice Liquid model. Some universal behavior was found, i.e., irrespective of reaction rate and grafting density, the width of the reaction front as well as the height of the front show for long times the same scaling with respect to time. During the formation of the polymer layer despite the observed difference in dispersion of chain lengths for different grafting densities and reaction rates at a given layer height, the quality of the polymer layer does not seem to depend on these parameters.

Bilateral Embedded Anchoring via Tailored Polymer Brush for Large-Area Air-Processed Blue Light-Emitting Diodes.

Perovskite light-emitting diodes (PeLEDs) that can be air-processed promises the development of displaying optoelectronic device, while is challenged by technical difficulty on both the active layer and hole transport layer (HTL) caused by the unavoidable humidity interference. Here, we propose and validate that, planting the polymer brush with tailored functional groups in inorganic HTL, provides unique bilateral embedded anchoring that is capable of simultaneously addressing the n phases crystallization rates in the active layer as well as the deteriorated particulate surface defects in HTL. Exemplified by zwitterionic polyethyleneimine-sulfonate (PEIS) in present study, its implanting in NiOx HTL offers abundant nuclei sites of amino and sulfonate groups that balance the growth rate of different n phases in quasi-2D perovskite films. Moreover, the PEIS effectively nailed the interfacial contact between perovskite and NiOx, and reduced the particulate surface defects in HTL, leading to the enhanced PLQY and stability of large-area blue perovskite film in ambient air. By virtue of these merits, present work achieves the first demonstration of the air-processed blue PeLEDs in large emitting area of 1.0 cm2 with peak external quantum efficiency (EQE) of 2.09 %, which is comparable to the similar pure-bromide blue PeLEDs fabricated in glovebox.

Superparamagnetic iron oxide nanoparticles functionalized with on-demand redox-responsive contractible coordination polymer brush as molecular actuator driven by π-dimerization

Nanomachines require molecular actuators to be coupled to a condensed phase. In this work, a redox responsive 1D contractible coordination polymer (ZnL) used as non-interlocked actuator is grafted onto superparamagnetic iron oxide nanoparticles (SPIONs) in a brush-like configuration. Oxidized rod-like ZnL oligomers have ability to reversibly self-fold upon reduction via π-dimerization of their bis-viologen units. Unlike in usual responsive brushes, ZnL chains behave individually, generating spatially controlled mechanical motion at nanoparticle surface associated to significant variations of particle diameters. ZnL oligomers were “grafted to” SPIONs in a single step. Reduction of colloidal dispersions was perform by visible light illumination with the help of a photoreductant. π-dimerization was assessed by UV–vis–NIR and reversible contraction of ZnL brush was characterized by DLS. Effects of ZnL chains length and grafting density on mechanism and performance of contractibility were studied. ZnL brush can alternately be contracted and extended with excellent reversibility. Combined UV–vis–NIR, DLS and TGA analyses demonstrate that π-dimerization is only intramolecular and that chains behave as independent actuators. Maximal contraction of 22 nm is obtained for largest particles (DH = 86 nm). Full to partial contraction of the brush depends on grafting density with a threshold at ≈ 47 chains per particle.

Rewritable Surface‐Grafted Polymer Brushes with Dynamic Covalent Linkages

AbstractSurface grafting of polymer brushes drastically modifies surface properties, including wettability, compatibility, responsiveness, etc. A broad variety of functionalities can be introduced to the surface via different types of polymers. Bringing together properties of two or more types of polymer brushes to one surface opens up even more possibilities in brush‐modified materials. However, while it is generally feasible to introduce several chemical compositions along the brushes via copolymerization, it is challenging to vary the types of polymer brushes along a surface. Although previous studies have demonstrated binary brushes via orthogonal polymerization techniques or partial deactivation/regrafting, they commonly limit the number of polymer types to two. Here, we propose a strategy to introduce dynamic covalent diketoenamine linkages at the root of polymer brushes. The grafting density could be precisely tuned during surface functionalization. The surface‐anchored polymer brushes were cleaved by the addition of small molecule amines. New polymer brushes can be regrafted from the surface following refunctionalization of exposed sites. The maneuverability allows tuning of the types and densities of the polymer brushes, pointing the way to the preparation of a new generation of well‐defined brush‐modified materials with mixed grafts, with potential applications in the design of smart materials and surfaces.

Polymer Brushes Synthesized by the "Grafting-through" Approach: Characterization and Scaling Analysis.

In this study, a combined morphological and scaling analysis of brushes synthesized by the "grafting-through" method was performed, and the possibility of regulation of the thickness was revealed on an example of polyacrylamide brushes. The chemical composition of the surface in the proposed three-step approach was analyzed by photoelectron and infrared spectroscopy. It was shown that the thickness of the dried brush can be tuned in a controlled manner by varying the polymerization temperature. The scaling dependence of the thickness of the dried brushes d on the length of the polymer d ∼ Lv was obtained by comparing reflectometry and dynamic light scattering data. The value of the exponent v = 0.82 corresponds to a rather high grafting density, exceeding the density of mushroom-like (ν ∼ 1/3) brushes and approaching the value for stretched polymer brushes (ν ∼ 1). A 10-fold increase in the polymer molecular weight leads to a slight decrease in grafting density by a factor of 2, which suggests that the "grafting-through" approach allows obtaining brushes with a high grafting density independently of attached polymer chain length. Herein, the possibility of attachment of uniform polymer brush on large substrates with this approach was demonstrated, which means the scalability of the "grafting-through" technique. The considered approach opens up a simple way for surface modification with polymer nanolayers of controlled thickness.

Machine Learning Aided Design and Optimization of Antifouling Surfaces.

Antifouling surfaces, renowned for their strong surface resistance to proteins, cells, or tissues in various biological and environmental conditions, have broad applications in implanted devices, antibacterial coatings, biosensors, responsive materials, water treatment, and lab-on-a-chip. While extensive experimental research exists on antifouling surfaces, machine learning studies on this topic are relatively few. This perspective specifically focuses on exploring the complex relationships between the composition, structure, and properties of antifouling surfaces, examining how these factors correlate with surface hydration and protein adsorption. Different machine learning models have been developed to analyze and predict single and multiple protein adsorptions on various types of surfaces, ranging from structureless surfaces to well-ordered and rigid self-assembled monolayers, dynamically ordered polymer brushes, and complex filtration membranes. These models not only identify key descriptors or functional groups critical for antifouling performance (surface hydration, protein adsorption) but also predict the antifouling properties for a specific surface. Recognizing current challenges, this perspective delineates future research directions in the antifouling field. By leveraging and comparing current machine learning approaches, it aims to advance both the design and fundamental understanding of antifouling surfaces, thereby pushing the boundaries of innovation in this critical field.

A Total Internal Reflection Microscopy (TIRM)-Based Approach for Direct Characterization of Polymer Brush Conformational Change in Aqueous Solution.

This study presents a novel approach utilizing total internal reflection microscopy (TIRM) to effectively characterize the swelling and collapse of polymer brushes in aqueous solutions. Zwitterionic poly(carboxybetaine methacrylate) (PCBMA) and nonionic poly[oligo(ethylene glycol) methyl ether methacrylate] (POEGMA) brushes are chosen as model systems. By investigation of an intriguing theory-experiment discrepancy observed during the measurement of near-wall hindered diffusion, valuable insights into the compressibility of polymer brushes are obtained, revealing their conformational information in aqueous solution. The results demonstrate that zwitterionic PCBMA brushes exhibit minimal antipolyelectrolyte effects in 0.1-10 mM NaCl solution but undergo significant swelling with increasing pH. On the other hand, nonionic POEGMA brushes exhibit similar responses to ionic strength as weak polyelectrolyte brushes. These unexpected findings enhance our understanding of polymer brushes beyond classical theories. The TIRM-based approach proves to be effective for characterizing polymer brushes and other soft nanomaterials.

Controlled Synthesis of Bioderived Poly(limonene carbonate)-Oligolysine Hybrid Macromolecules.

A straightforward and stepwise functionalization of poly(limonene carbonate) (PLC) was achieved through the use of thiol-ene click chemistry introducing primary amine groups. These amines are initiating points for N-carboxy anhydride (NCA) ring-opening polymerization (ROP) reactions, allowing us to modify the PLC backbone with oligolysine fragments, thereby creating a polymer brush type macromolecule. These newly prepared biohybrid structures show a clear hydrophilic behavior as evident from their physical behavior and contact angle measurements.

Rapid Construction of Liquid-like Surfaces via Single-Cycle Polymer Brush Grafting for Enhanced Antifouling in Microfluidic Systems.

Liquid-like surfaces have demonstrated immense potential in their ability to resist cell adhesion, a critical requirement for numerous applications across various domains. However, the conventional methodologies for preparing liquid-like surfaces often entail a complex multi-step polymer brush modification process, which is not only time-consuming but also presents significant challenges. In this work, we developed a single-cycle polymer brush modification strategy to build liquid-like surfaces by leveraging high-molecular-weight bis(3-aminopropyl)-terminated polydimethylsiloxane, which significantly simplifies the preparation process. The resultant liquid-like surface is endowed with exceptional slipperiness, effectively inhibiting bacterial colonization and diminishing the adherence of platelets. Moreover, it offers promising implications for reducing the dependency on anticoagulants in microfluidic systems constructed from PDMS, all while sustaining its antithrombotic attributes.

Biomimetic joints inspired soft and hard combined 2D diamond solvent-free nanofluids with multi-layer structure for superior lubrication

The articulating joints consist of a three-layer lubricating structure, which combines soft and hard materials, including cartilage, polymer brushes, and a hydration layer. This structure leverages the synergistic effects of fluid and boundary lubrication to maintain ultra-low friction under different pressures on the same frictional surface. In this study, a biomimetic multilayer lubricating structure inspired by joint tissues is constructed using single-crystalline diamond nanosheets (SCND) as the hard phase material. Through a facile chemical reduction method and employing polydopamine (PDA) as a "bridge", a soft phase material is deposited onto the SCND surface to produce diamond composite silver nanocomposites (SCND@PDA@Ag). Subsequently, two solvent-free SCND@PDA@Ag nanofluids are prepared by grafting organic canopy substances onto the SCND@PDA@Ag surface via ionic bonds or covalent bonds, referred to as SCND@PDA@Ag-ionic bonding nanofluid and SCND@PDA@Ag-covalent bonding nanofluid, respectively. The findings reveal that the SCND@PDA@Ag-covalent bonding solvent-free nanofluid exhibits superior lubricating performance for steel/SiC contacts. The friction coefficient and wear rate for steel/SiC are significantly reduced by 93.2 % and 63.1 %, respectively, compared to dry friction, it's noteworthy that these results outperform those achieved by individual components of the lubricant. During the friction process, SCND and silver particles on the surface of SCND@PDA@Ag-covalent bonding solvent-free nanofluid work together to enhance lubrication synergistically. Furthermore, silver particles on the surface of SCND are released and fill into the worn surface, providing a repairing effect. This study highlights that the design of soft-hard multilayer structures offers a novel approach for researching nanocomposite materials in the field of tribology.

Inhibition of bacteria adhesion and biofilm formation using a precisely structured nitric oxide-releasing coating with repeatedly renewing antimicrobial and antifouling ability

Bacterial adhesion and colonization usually causes the formation of biofilm that cannot be easily eradicated by common antibiotics and disinfectants. Surface covalent immobilization of nitric oxide (NO)-releasing polymer is an effective surface modification strategy to combat the threat from bacteria. Although surface covalent strategy avoided the leaching of toxic NO donors, the existence of hydrophobic NO donors on topsurface could inevitably accelerate the microorganism adhesion and accumulation, and the NO-releasing period of time was still very limited. In this work, we prepared an antimicrobial and antibiofilm surface via tethering a precision-structured NO-releasing copolymer brush to an organic-inorganic hybrid hard coating (> 5H pencil hardness) on one end. The precision-structured diblock copolymer brush was composed of a surface antifouling block and a subsurface antimicrobial block of NO-releasing units. A typical effect of “kill two birds with one stone” was observed, the NO releasing subsurface segment within a polymeric matrix prolongs NO release while also preventing surface fouling caused by hydrophobic NO donors on top surface. The impacts of polymer architecture on bioactivity was detailed investigated, and the block copolymer brush exhibited the optimal inhibitory effects against bacteria colonization and biofilm formation. The developed bioactive diblock copolymer brush was grafted from a hard hybrid persistent coating that embeds considerable initiation sites for surface modification. Thanks to the presence of initiator throughout the hybrid network, the initiation layer could initiate polymerization repeatedly after the polymer brushes are worn off at high pressure. Thus, the coating exhibited repeatedly renewing antimicrobial and antifouling ability after multiple abrasion cycles. This work not only developed a novel strategy for regulating NO releasing via modulating the polymer architecture, but provided a feasible route for obtaining a robust initiator layer for synthesizing polymer brush for antimicrobial and antifouling applications.

‘Clickable’ polymer brush coated magnetic nanoparticles: Employing Diels-Alder and azide-alkyne cycloaddition for modular targeted drug delivery platforms

Effective methods of multi-functionalization of nanomaterials are essential for fabricating effective targeted drug delivery systems. Herein, we disclose the fabrication of polymer brush-coated magnetic nanoparticles that could be functionalized with drugs and targeting ligands through orthogonal click reactions. In particular, polymers containing electron-rich furan groups as functionalization handles are grown from the surface of magnetic nanoparticles using the ‘graft-from’ approach. Furthermore, azide groups are installed at the chain end of polymer brushes to furnish an orthogonally functionalizable system. The attachment of maleimide-containing fluorescent dyes and cytotoxic drugs using the Diels-Alder reaction is demonstrated. Drug-conjugated nanoparticles functionalized with integrin-targeting peptide using the azide-alkyne cycloaddition reaction undergo preferential uptake in cancer cells and show dose-dependent cytotoxicity. We envision that the modularly functionalizable system disclosed here could target various cancer cells using an appropriate combination of drugs and targeting groups.

Synthesis of a perovskite surface-coated polymer brush by photo-induced atom transfer radical polymerization

Lead halide perovskite nanocrystals (PNCs) are expected to be applied in the field of optoelectronics due to their color tunability, high color purity, and near-unity photoluminescence quantum yields. Moreover, the construction of nanocomposite structures with functional polymers has been reported to improve the material stability as well as the ordered structure with high orientation and periodicity. In this study, we demonstrated the synthesis of polymethyl methacrylate (PMMA) on the PNCs by surface-initiated polymerization. We synthesized PMMA polymer brushes by photo-induced atom transfer radical polymerization (p-ATRP) after coordinating the initiator on the PNC surface. We succeeded in obtaining PMMA-PNCs with a degree of polymerization of 21. Moreover, thermal stability tests showed that PMMA-PNCs achieved improved thermal stability compared to pristine-PNCs. This work can provide guidance for developing polymer brush-PNCs via surface-initiated polymerization.

Immobilization of Protein Probes on Biochips with Brush Polymer Cells

Immobilization of Protein Probes on Biochips with Brush Polymer Cells

Swelling and Degrafting of Poly(3-sulfopropyl methacrylate) Brushes.

Upon exposure to a good solvent, polymer brushes prepared via surface-initiated polymerization can undergo degrafting via cleavage of bonds that anchor the polymer tethers to the underlying substrate. As polymer brushes are often used in a solvent swollen state, this has implications for the longevity of these polymer coatings. Improving the fundamental understanding of this process is thus also of practical importance. It is believed that degrafting is the consequence of tension amplification at the bonds that anchor the polymer grafts, which is driven by swelling of the polymer brush film. Taking advantage of the sensitivity of the swelling behavior of poly(3-sulfopropyl methacrylate) (PSPMA) brushes toward changes in ionic strength, this study has investigated the degrafting behavior of these brushes in aqueous media at different LiCl and NaCl concentrations. The aim of these experiments was to investigate whether the rate constant of the degrafting process was correlated with the swelling ratio of the PSPMA brushes. The experiments show that in aqueous LiCl solutions, the initial rate constant of the degrafting process is correlated with the swelling ratio of the PSPMA brush. This observation represents a first example of the correlation between these two parameters for hydrophilic polymer brushes in aqueous media and supports the idea that degrafting is a mechanochemical process driven by a swelling-induced tension at the polymer-substrate interface.

Carbon dots grafted by oil-soluble polymer brushes derived from bis-alkyl chain monomers as a lubricant additive of poly-α-olefin with outstanding friction-reducing, anti-wear and anti-rust properties

The application of carbon dots (CDs) as lubricant additives of nonpolar oils such as poly-α-olefins (PAOs) has been greatly hindered because most of CDs derived from the bottom-up method were water-soluble. In this work, the oil-soluble polymer brushes grafted CDs were synthesized by the surface-initiated atom transfer radical polymerization of bis-alkyl chain monomers. As expected, the polymer grafted CDs exhibited the excellent long-term dispersion stability in PAO owing to the principle of similar compatibility. As the lubricant additives of PAO4, the CDs showed the best friction-reducing and anti-wear properties when the polymerization time was 2 h. Adding 1 wt% of CDs could make the coefficient of friction and wear volume of PAO4 reduce by 64.1 % and 49.6 %, respectively. Moreover, both the tribological properties and anti-rust performance of CDs were superior to the commercially used ZDDP. The distinguished friction-reducing and anti-wear properties of CDs were attributed to the synergistic lubrication of carbon cores and polymer brushes. The rolling, repairing and polishing action of carbon cores, together with the tribo-reactions of polymer brushes, resulted in the formation of tough lubricating films on the rubbing surfaces, thereby tremendously alleviating the friction and wear of tribopair. The impressive anti-rust performance of CDs could be assigned to their strong adsorption ability on metallic surfaces. The above results are hopeful to provide useful information for the design and development of efficient multifunctional additives such as polymer-grafted metallic or inorganic nanomaterials.